The present invention relates generally to memory or logic arrays and more specifically to an improved redundancy for memory or logic arrays.
In order to increase yield in memory and logic arrays, it has been suggested that redundant rows be provided. These rows include their own separate decoder having programmable elements in the decoder such that the row may be programmed to decode a defective row identified by testing. The decoder is connected to the row by a row driver. The programmable elements of the decoder are generally fuses which are blown to appropriately address the decoder using a pad which provides voltage across the fuses with the appropriate addresses provided to the input of the decoder. In prior art redundant row schemes, the redundant row and row driver are not properly isolated from the programmable decoder. The row is connected to the decoder and discharged to ground through the decoder. This produces undesirable currents through the programmable decoder. Also, for certain kinds of fuses, specifically metal fuses, grow-back of the blown fuses has occurred through metal migration because of the voltage applied across the programmed fuse when that line was addressed in combination with the voltage available from the line driver.
Thus, it is an object of the present invention to provide a redundant row scheme which protects the programmable decoder from the row drivers and the row line.
Another object of the present invention is to provide a scheme for redundant rows which prevents grow-back of programmed metal fuses in a programmable decoder.
Still another object of the present invention is to protect the row decoder from the row capacitance in a redundant row system.
These and other objects of the invention are attained by providing a protection circuit between the programmable decoder and the line driver of a redundant row system which provides a path to ground for discharging the row line and limits the voltage across the programmable decoder to prevent grow-back of the programmed fuses.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.